1. Field of Invention:
The invention is directed generally to safety equipment. In particular, the invention is directed to safety relay which maintains or locks the contacts of an electromechanical relay in the desired position.
2. Description of Related Art:
Reliability is an essential characteristic of safety equipment. Electromechanical relays are designed to operate the electrical circuits of safety equipment through a set of contacts. In such applications, the relay initiates a chain of events which brings the connected safety equipment to a safe state or stable condition. It is important that such relays maintain the equipment in the safe or stable condition until a change is positively initiated by the operator or computer.
Some commercial relays, as shown in FIGS. 1 and 2, employ a single coil 10, located within a magnetic frame 12, which when energized, draws an armature 14 and attached contacts (not shown) downwardly against the bias of a kickout spring 16. The armature 14 bottoms out on a lower or fixed pole 18 located on a central frame portion 20, which extends into the center of coil 10, as shown. A non-magnetic disc 22 is provided in order to reduce the hold down force on the fixed pole face 24 of the armature 14 to separate from the pole face 18 when the coil voltage is reduced to a predetermined value (e.g. 12 to 15 volts DC). In the position shown in FIG. 1 the electromagnetic forces generated by the coil 10, holds down the armature 14 and the electrical contacts (not shown) in the desired or closed position. When the coil 10 is de-energized (FIG. 2), the kickout spring 16 moves the armature 14 upward against the force of gravity to change the relay to its open position. In the design of such relays, when deenergized, the armature 14 is held in the up position only by the force of the kickout spring 16. Under such conditions the relay is susceptible to shock and vibration and may fail to maintain the contacts in the desired safe state.